The present invention relates generally to methods and apparatus for improving the addressability, and thus the reliability with which data written to DVD−R/RW and DVD+R/RW media is recovered. Aspects of the invention relate more particularly to improving the search for the wobble sync pattern, thereby improving the bit error rate at the output of the Land Pre-Pit (LPP) or ADdress In Pre-groove (ADIP) decoder of the DVD recorder. Other aspects of the invention relate more particularly to improving the ability of the DVD recorder to accurately locate DVD user data structures relative to the predefined structures of DVD−R/RW and DVD+R/RW media provided for locating information written thereon.
There are two principal standards for recordable and rewritable DVD media that are conventionally in use today. They are referred to as DVD−R/RW and DVD+R/RW. Some relevant features of these types of media are provided here.
Information is recorded on a surface of DVD−R/RW media on a track, 100, defined by a spiral groove, 101, bounded by raised areas called lands, 102, 103. (See FIG. 1.) User information is written in the groove, 101, as a series of marks and spaces defined by regions of high and low relative reflectivity. The lands, 102, 103, that bound the grooves include features R1, R2, R3, 104, 105, that represent certain address information and medium-related parameters, such as the power required to read and/or write the user information.
The spiral groove, 101, defined by the lands 102, 103, follows a spiral path on which is superimposed a substantially sinusoidal, radial wobble (R1, R2, R3, for example) having a fixed frequency and amplitude along the entire track of the medium. The wobble represents position information along the track, required to use the DVD−R/RW media. Read and write clocks and disk rotation speed control may all be derived from recovered wobble information. In addition, superimposed on the wobble at predetermined, fixed locations are microscopic pits formed in the lands called Land Pre-Pits (LPPs), 104, 105. The location of frame synchronization information and other sector heading information within the user data is defined by the locations of certain predetermined sequences of LPPs, 104, 105. The significance of the predetermined sequences of LPPs when decoded and represented in binary form, referred to herein as LPP symbols, is defined by the following Table, in which the LPP symbol is comprised of three binary digits or bits identified as b0, b1 and b2.
TABLEDefinitionb2b1b0EVEN SYNC111ODD SYNC110Pre-pit DATA ONE101Pre-pit DATA ZERO100
The features defining the tracks, including the lands, the grooves and the LPPs may be embossed or otherwise formed on the media together.
The relationship of LPP symbols to the structure of DVD−R/RW media is now explained. The basic structural unit by which data are represented is a channel bit duration, T. Hierarchically, the next level of structure is the frame, which includes 1,488 channel bit durations, i.e., 1,488.T. One LLP symbol is associated with each pair of frames and 26 frames comprise a DVD−R/RW sector. DVD−R/RW user data is protected by a level of redundancy provided by an error correcting code (ECC) that operates on a structure called an ECC block. Each ECC block includes 16 DVD sectors.
The wobble signal is recovered using a quadrant detector, whose outputs are then combined algebraically to produce a substantially sinusoidal wobble signal. When the head passes over an LPP, an LPP spike, also referred to as an LPP pulse, is superimposed on the substantially sinusoidal wobble signal. LPPs are located at positions selected to produce LPP pulses at peaks of the sinusoidal wobble always having the same polarity (+/−).
The presence and meaning of the sequence of LPP symbol bits is determined by detecting the locations of the spikes on the wobble signal. The predetermined sequences of bits recovered are mapped to a meaning according to the foregoing Table.
The features defining the tracks, including the lands, the grooves and the LPPs may be embossed or otherwise formed on the media together, at the time of manufacture.
The wobble signal is recovered using a four-quadrant photo detector, whose analog signal outputs are then combined algebraically by any suitable analog or digital signal processing to form the radial push-pull signal. While the head is following a track, the radial push-pull signal is the substantially sinusoidal wobble signal, 201. (See FIG. 2A.) When the head passes over an LPP, a spike, 202, is superimposed on the substantially sinusoidal wobble signal. LPPs are located at positions, 203, corresponding to peaks of the sinusoidal wobble always having the same polarity (+/−). Thus, the LPP spikes 202 are data pulses added to the underlying wobble signal 201 at particular locations.
The meaning of the sequence of LPPs is determined by detecting LPP symbols comprised of sequences of the presence or absence of the spikes on the wobble signal at particular locations, and decoding the sequence symbols into more complex meanings.
As indicated above, LPP information is embossed or otherwise prerecorded on DVD−R/RW media, other than when a user records data, for example during manufacture. The prerecorded LPP information carries various information used during subsequent recording of user data on the DVD−R/RW media. In order to successfully record user data in a manner permitting subsequent reliable recovery, the LPP spikes must be reliably detected. The amplitudes of the LPP spikes appearing on the wobble signal depend on many factors. The large number of factors which can vary the amplitudes of the LPP spikes tend to make a precise prediction of the average LPP spike amplitude difficult. Among the many factors, one important factor is significant variation in the amplitude of the quadrant photo detector signal output, especially variation in amplitude between different operating modes, such as between reading, erasing and writing operations. Laser power levels are highest during the write operation and lowest during the read operation. Due to the way DVD−RW media behaves while being erased, additional variations occur in optical pickup output as DVD−RW media traverses from the recorded to the erased state.
A conventional wobble Phase-Locked Loop (PLL) is shown in FIG. 3. The wobble PLL, 300, includes a phase detector, 301, a loop filter, 302, a voltage controlled oscillator (VCO), 303, and a wobble clock divider, 304. The output of the VCO, 303 is the write clock, 305, used to time the writing of user data. Because the write clock frequency is a multiple of the wobble signal frequency, the write clock, 305, is divided by the wobble clock divider, 304, to form the wobble clock, 306, before being compared in the phase detector, 301, to the reference wobble signal, 307, recovered from the disk. The value by which the wobble clock divider, 304, divides the write clock, 305, depends on the media type in use. For example, the wobble clock divider, 304, divides by 32 for DVD+R/RW media, while it divides by 186 for DVD−R/RW media. The phase detector, 301, produces a phase error signal, 308, which is filtered by the loop filter, 302. The filtered error signal, 309, which is produced by the loop filter, 302, controls the frequency of the write clock generated by the VCO, 303. The phase detector, 301, and the loop filter, 302, may be implemented in software, firmware or special purpose hardware, for example. In the case of the conventional wobble PLL shown, the phase detector, 301, and the loop filter, 302, are implemented as sequential logic clocked by the write clock, 305.
User data on DVD−R/RW and DVD+R/RW media is written in eight-to-fourteen modulation (EFM). Consequently, the synchronization symbol for user data is known as EFM sync. According to the DVD−R/RW standards, as shown in FIG. 4, EFM sync 401 should be written so as to be centered on the location of the LPP that when decoded represents LPP symbol bit b2 402. The LPP sync symbols 403, together with the data represented by the LPP data symbols 404, provide a robust absolute addressing method, whereby EFM frames of user data may be readily written to correct locations.
DVD+R/RW media also include tracks with a superimposed wobble, similar to the tracks of DVD−R/RW media; however, there are several important differences. DVD+R/RW media does not use LPPs to encode structural information about the media or locations along the track. Rather, predetermined portions of the track wobble are phase modulated so that the track wobble signal is correspondingly phase modulated to form so-called ADdress In Pre-groove (ADIP) information units. See FIG. 2B, which shows the modulation patterns of ADIP sync, ADIP data 1 and ADIP data 0. The ADIP unit is eight cycles of phase modulated wobble signal representing ADIP sync, ADIP data 1 and ADIP data 0. Like the LPP sync symbol in DVD−R/RW media, the location of the ADIP unit defines locations along the track. In DVD+R/RW media, as shown in FIG. 5, EFM sync 501 follows the start of the ADIP unit 502 by exactly 16 wobble signal periods.
Various kinds of defects in the media can make it more difficult to recover the synchronization information and the location information from the wobble signal on both DVD−R/RW media and DVD+R/RW media. Manufacturing defects, the use of embossing masters beyond their rated life, smudging and micro-scratches on the surface of a disk, and other defects can cause dropouts and drop-ins of the wobble signal. Dropouts and drop-ins, which are abnormally low amplitude or abnormally high amplitude regions in the wobble signal, can result in phase errors when the reference wobble signal is compared to the recovered wobble clock. Moreover, dropouts and drop-ins can cause missing, phantom or garbled sync information to be recovered from the wobble signal, whether that information is represented by LPP symbols superimposed on the wobble signal or whether that information is represented by ADIP phase modulated regions of the wobble signal.
One example of a system and method for better matching the write clock of a DVD recorder to information already present on the DVD to be recorded is disclosed by Kuroda in United States Patent Application Publication US2003/0039186 A1. Kuroda discloses resynchronizing write and read operations after data recording has been stopped and then restarted. Kuroda is concerned with seamlessly restarting the write process after a block has been written and the write process terminated. Notably, Kuroda does not solve or even address the problem of dropouts or dropins in the wobble signal recovered from a defective region of a DVD.